Topical cosmetic compositions are commonly formulated to provide one or more desirable properties. One of these properties, common to many cosmetic compositions, is skin moisturization.
Moisturization is typically imparted to these compositions by using one or a combination of two well-known technologies: including a humectant, such as glycerin or sorbitol, to hydrate the skin and prevent water loss, and/or forming a barrier against moisture loss by including substances such as petrolatum or heavy oils.
While these technologies are effective, each has drawbacks. For example, humectants can be sticky and tacky, must be used in relatively high concentrations to be effective, work only on the surface of the skin, and are easily washed off. Barrier-forming ingredients, on the other hand, are marginally effective, feel greasy and oily, and, like humectants, wear off a short time after application onto the skin. Among other drawbacks, neither technology provides for relatively long-term skin moisturization.
Other moisturizers are designed to work at the cellular level by rebuilding or preventing damage to the skin's natural barrier layer. Central to this barrier layer is the outermost layer of the epidermis, referred to as the horny cell layer (i.e., the stratum corneum). This layer provides primary protection against skin damage due to ultraviolet light and other environmental influences, and also acts to prevent excessive dryness.
The horny cell layer, however, is continually worn down due to contact with the environment and, therefore, must be constantly renewed. While this renewal occurs naturally, renewal can be interrupted by various endogenous and exogenous factors. When interrupted, the barrier layer's ability to function properly is impeded because dead, dull skin cells undesirably do not slough off regularly, and the natural lipids in the horny cell layer, such as ceramides, cholesterol, esters and the like, cannot properly control the amount of moisture evaporating from the epidermis.
Illustrative of these exogenous factors is ultraviolet light. Ultraviolet light can initiate a chain reaction that transforms lipids in the horny cell layer into free radical species. The free radical species, once formed, attack other lipids in the horny cell layer, thereby forming more free radical species which, in turn, results in the damage of more lipids. As more lipids are damaged, the skin's natural moisture barrier loses its ability to effectively regulate moisture retention in the skin. The damaged natural lipid layer permits more moisture to escape from the skin than is absorbed into the skin, resulting in dry skin.
Moisturizers acting at the cellular level are designed to penetrate the surface of the skin and repair the natural lipid layer, e.g., by facilitating the ability of dead, dull skin cells to slough off more regularly and/or by acting as free radical scavengers to prevent the free radicals from continuing the deleterious chain reaction.
Despite the availability of cosmetic moisturizing compositions, a need exists for topical cosmetic compositions that provide, among other beneficial properties, enhanced skin moisturization over an extended period of time without sacrificing after-feel, e.g., the skin is not rendered oily and greasy.